patch for mkdirs on camera path json filepath (#2502)

fix camera path json mkdir in viewer beta

Author: kerrj

nerfstudio/viewer_beta/render_panel.py

@@ -625,6 +625,7 @@ def _(event: viser.GuiEvent) -> None:
 
         # now write the json file
         json_outfile = datapath / "camera_paths" / f"{render_name_text.value}.json"
+        json_outfile.parent.mkdir(parents=True, exist_ok=True)
         with open(json_outfile.absolute(), "w") as outfile:
             json.dump(json_data, outfile)
         # now show the command